I agree, but a total ban on adding anything statwise is what's RAW.
Citation? I need to see exactly what you're using to reach that conclussion
Windows have stats, and if you share the RAW IS LAW view, then you can't even do that.
Friends don't let friends play at a table that's that bad.
I'd say there is some vague line somewhere between RAW and coming up with grudge monsters, but that's not strictly legal and is theoretically badwrong.
We are allowed, and even encouraged, to let the players use creative solutions. That does not somehow equate to a backdoor ban on anything creative by saying you can't interact with something I don't have stats for.
Talk to the bad guys? Sorry. Don't have a starting attitude.
Climb the wall? Sorry, no climb DC.
Cut through the wall? Sorry, don't know the hardness
And to use the rest of RAW, the only creative solutions that can be done are to avoid encounters... not to have new unpublished encounters.
If you're including a door as an encounter it becomes impossible to have creative solutions that won't do this, somehow. No, you can't throw more monsters, different monsters etc at the party, but if they want to climb in the window you can set a climb dc for the wall and a disable device for the lock.
Little things like that are the required secondary powers of creative solutions. Banning them bans creative solutions.